Browsing by Author "Sammet, Manfred"

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    Characterization and structural aspects of fluorophosphate glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1985) Sammet, Manfred; Brückner, Rolf
    Nine homologous series of fluorine phosphate and one series of pure phosphate glasses of laser glass types have been prepared and characterized by determining the linear and non-linear refractive values and dispersion, the glass transition temperature Tg, thermal expansion (TE), density ϱ, and anion mole volumina (MV). The results are discussed with respect to structural aspects. Apart from principal differences in the absolute properties and structure, an analogous behaviour is found for the cations in the fluorine phosphate glasses compared with pure phosphate glasses. The specific structural influence of the cations (Na+, Mg2+, Ba2+, Al3+, P5+, V5+) is generally larger than that of the fluoride ions at ratios F/O from 0,9 to 1,8, indicating that fluorine has not only network modifying but also remarkable network forming qualities.
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    Infrared absorption and structural investigation of fluorine phosphate and phosphate glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1987) Sammet, Manfred; Brückner, Rolf
    Structural conclusions are obtained for various homologous series of the above-mentioned glasses by IR spectroscopy. Alterations in vibration frequencies of the fluorine phosphate tetrahedra as a function of chemical composition are interpreted and indicate, that fluorine ions are present in the glass network as POnF4-n units. P-F vibrations show the participation of fluorine in the phosphorus coordination with network forming character. Another remarkable influence of the fluorine ions is the delocalization of the P = O double bonding, which is typical and localized for pure phosphate glasses, and thus, only bridging and non-bridging oxygen atoms are left in the fluorine phosphate glasses. This delocalization is connected with an increase in frequency of all remaining P-O vibrations (stronger P-O bondings), which prevents the phosphorus atoms from carrying a higher charge. Neighbouring aluminum atoms get a chance for a four-fold coordination without the presence of alkali ions by a charge transfer from P5+ to Al3+ via the p-orbital of oxygen. From other frequency shifts is evident the network forming influence of Al3+, Mg3+ and the network modifying character of Na+, Ca2+ and Ba2+.